Most walls built are hollow. A typical interior wall is formed with wood or metal stud framing on certain centers with large sheets of gypsum or plasterboard secured to the framing. The seams in the board are taped and finished, and the wall is then painted or papered. Ceilings may be formed by boards secured to rafters and finished in the same way.
Holes are sometimes made in such walls or surfaces, such as by a door knob punch out, other accidents, or even maliciously. While small holes such as those used for picture hooks are easy to repair, larger holes or punchouts are not.
There are two generally employed methods of repairing such larger holes. One is to secure a tape-like patch over the hole and then smooth a plaster compound or grout over the patch. When it dries, the wall is repainted or papered. Unfortunately, the spot soon becomes visible. The repair spot also cannot withstand any contact pressure. It is so weak, a person could put a finger through the wall, and any significant contact distorts the wall and finish. Such repair systems simply are not a restoration of the wall or surface. They are cosmetic and of short life.
Another repair system is to remove or cut out a section of the board which includes the hole and replace it with a sized cut section spanning the centers of adjoining studs. The replacement section is usually rectangular having a width dictated by the stud centers and a height dictated by the size of the hole. When the repair section is in place, the seams are taped and troweled as with the installation of new board. While the seams along the stud centers are generally reliable because of the stud support, the seams spanning the studs are not. Any pressure against the insert section will soon make the top and bottom or spanning seams visible distortions marring the appearance of the wall.
The most desirable way to repair walls would be to restore the gypsum or plaster material to the hole. While plaster can be applied with a trowel or spatula to smooth over the wall surface, the hollow nature of the wall makes this impractical. Without an interior plug, form, or backstop, the plaster would literally fill the hollow wall cavity and entomb anything inside the wall such as wiring or outlet boxes.